linux-kernel - Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

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Message-ID: <4BBB466D.3090705@redhat.com>
Date:	Tue, 06 Apr 2010 10:34:21 -0400
From:	Rik van Riel <riel@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Minchan Kim <minchan.kim@...il.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

On 04/06/2010 06:09 AM, KOSAKI Motohiro wrote:
>> (b) is also impossible. SLAB_DESTROY_BY_RCU delay the page for anon_vma
>> freeing until next rcu period. It mean rcu_read_lock()+page_mapped()
>> can see kfree()ed page. but it is safe. noone corrupt it.
>
> by the way: I haven't understand why rik's per process anon_vma concept
> works correctly with ksm. ksm increase anon_vma->ksm_refcount. but it seems
> not guranteed vma->anon_vma and page->anon_vma are the same.

KSM removes the page from its original anon_vma.

If the page gets reinstantiated (copy on write), it will be
created in the vma->anon_vma.

Am I overlooking something?
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